You can make a copy of your site in the site settings.
Tip: if you are looking for a way to backup your current site, make sure to check the article Site history.
Duplicating a site
For that, log in to your account and hover over to the needed site preview.
Click on three dots near the site preview and choose Duplicate in the drop-down menu:

...or open the General info tab in the Settings of your site, scroll down to the Website Actions and click Duplicate:

Enter the name for the copy of your current site and click Save duplicate:

Note: a copy will act independently from the original site, so all the changes to the sites will have to be done separately.
Tip: if you are looking for a way to backup your current site, make sure to check the article Site history.
Duplicating a site
For that, log in to your account and hover over to the needed site preview.
Click on three dots near the site preview and choose Duplicate in the drop-down menu:

...or open the General info tab in the Settings of your site, scroll down to the Website Actions and click Duplicate:

Enter the name for the copy of your current site and click Save duplicate:

Note: a copy will act independently from the original site, so all the changes to the sites will have to be done separately.
Published on: 12 / 12 / 2019